Wormy Turnips and Coffee Grounds

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Turnips and Coffee Grounds

Q: Lucy Lambert: I have heard that when a person plants turnip seeds with coffee grounds that this prevents a wormy turnip. Is this true? If not what could one use?

A: Bottom line? No – coffee grounds won’t cure a wormy turnip, but here’s what you need to know:

Cabbage maggots larvae attack turnips, rutabaga, cabbage, cauliflower, broccoli, and radishes.  These maggots emerge from the soil in mid May (the same time that the Saskatoons flower) in the form of small, gray flies that lay white eggs at the base of stems and on the soil.

It takes less than a week for the eggs to hatch horrid little legless maggots that go straight back into the soil to gobble up the roots of their favourite veg.

Newly-planted seedlings quickly turn yellow and die, then they come back in a little more than a month as a fly to repeat the cycle for a second time!

Control Options

The best control is exclusion! You can protect the beds from the flies where seeds have been planted with cheesecloth, re-may fabric, or nylon sheeting. You need to leave it on from the time the saskatoons flower – from mid-May until the end of June to eliminate the 1st and 2nd life cycles.

Don’t plant cole crops in the same place. Completely clear out maggot infested crops and roots (rather than shredding and rototilling under the decimated plant remains).

Once cabbage maggot damage is noticed, it is too late to apply control procedures. Since the first generation of cabbage maggots is the most damaging, planting seeds or transplants after the peak of adult emergence (wait until June) and egg laying in the spring may provide the best control.

High Tech Approach:  Commercially, growers estimate peak emergence by accumulating degree-days after the ground has thawed (e.g., beginning April 1st). The daily formula to use is: (Max. temperature + min. ambient temperature/2) – 43 F. Peak emergence of the first three generations will occur when 300, 1475, and 2650 degree-days have accumulated, respectively. Plant afterwards.

Chemical Control

The available chemical options are preventative; no insecticides are labelled for use once an outbreak is underway.

Cultural Control

Adult cabbage maggot flies are probably attracted to rotting organic matter and freshly rototilled gardens. Avoid ploughing fresh animal manure, weeds, green manure, or other cover crops in spring. If there is a winter cover crop, plough it at least 3-4 weeks before planting.

Ploughing crops in fall is better than ploughing crops in spring because the cabbage maggot flies are more attracted to live, green organic matter incorporated into the soil.

If cole crops are directly seeded, use a drag chain behind the planter to eliminate any moisture differences in the soil between the seed row and the adjacent soil. Moisture from newly planted seed rows can attract cabbage maggots.

Biological Control

Naturally occurring soil-inhabiting fungi may attack and decrease cabbage maggot larval populations. Predaceous ground beetles also eat cabbage maggot eggs, larvae, and pupae. Parasitic wasps also help to reduce cabbage maggot population. At the present time, there are no commercially available biological control options

Coffee Grounds

Used coffee grounds are reported keep bugs at bay by acting as a repellent for snails and slugs (not cabbage maggots).

Used coffee grounds are high in acid, and a natural fertilizer for plants that like foods high in acid, such as evergreens, azaleas, rhododendrons, and blueberries. The grounds also provide nitrogen to your garden.

The worms love the coffee, too. They will eat the grounds and produce a nice, fertilized compost.

How Recycled Coffee Grounds Work in the Garden

In addition to obvious things like water and light, most plants need nitrogen to grow. The nitrogen’s job is to keep the green parts green.

The coffee grounds contain about 2% nitrogen, .03% phosphoric acid, and a bit of potash. The typical chemically created fertilizer you would find in the store would look something like 10-10-5, or 10% nitrogen, 10% phosphorus, and 5% potassium.

The grounds work like a slow-release fertilizer. Each time it rains, the nitrogen and acids leach out and fertilize your plants.

Recycling your coffee grounds is easy! Simply spread your coffee grounds around the base of your acid-loving plants.

You can leave the grounds on top, or you can mix them in to the top two or three inches of soil. You can also mix your grounds in with your compost, just keep the grounds to less than 25% of the mixture, or it will become too acidic.